1. Field of The Invention
The invention relates to an apparatus for recording a digital information signal in tracks on a record carrier, the digital information signal being an information signal comprising subsequent transport packets of information, the apparatus comprising:
input means for receiving the digital information signal,
signal processing means for processing the digital information signal so as to make the digital information signal suitable for recording in said tracks, the signal processing means being adapted (a) to generate sync blocks of information, each sync block comprising a first block section which comprises a synchronization signal and a second block section comprising a number of information bytes of the digital information signal, (b) to store, each time, the information included in x transport packets of the digital information signal in the second block sections of a group of y sync blocks, the second block section of at least the first sync block of the group of y sync blocks comprising a third block section for storing a time stamp,
time stamp generator means for generating time stamps for packets of the digital information signal, and comprising counter means adapted to generate subsequent cycles of count values,
sync block number generator means for generating sync block numbers for each of the sync blocks, and
writing means for writing the sequence of sync blocks in the tracks on the record carrier, at a predetermined recording speed of the record carrier, the writing means comprising a rotatable head drum provided with at least a first and a second writing head, the digital information signal being meant for reproduction in a reproduction apparatus at a trick play speed which equals n1 times said recording speed, where n1 is an integer larger than 1.
2. Description of the Related Art
Such a recording apparatus is known from U.S. Pat. No. 5,579,183, document D1 in the List Of Related Documents. The known apparatus takes the form of a digital video recorder for recording a digital video signal. The digital video signal may be in the form of an MPEG-encoded video signal, in which packets of information of the digital video signal are included in the serial data stream of the MPEG-encoded video signal. In addition to such MPEG-encoded video signal, a trick play signal can be recorded in the tracks on the record carrier. Such trick play signal can be the same video signal, but reproduced at a record carrier (trick play) speed which is other than the nominal reproduction speed. Generally, a separate datastream is recorded as the trick play signal on the record carrier for enabling the reproduction at such trick play speed. The trick play signal can be derived from the MPEG-encoded video signal, e.g., by selecting I-frames from the MPEG-encoded video signal. The digital information signal defined hereunder in the claims is meant to be this trick play signal.
This trick play signal, however, need not necessarily be a trick play signal that has a relationship with the MPEG-encoded video signal, but can be a completely different signal. But, in the same way as the MPEG-encoded digital video signal, the serial datastream of the trick play signal comprises packets of information of the trick play signal.
The document mentioned above describes the inclusion of time stamps in the packets in all the serial datastreams recorded on the record carrier, in order to enable a correct regeneration of the serial datastream of packets, with the correct mutual timing relationships between the subsequent packets in the serial datastream, so that a correct decoding in an MPEG decoder will be possible. In order to realize this, the reproducing apparatus for reproducing an MPEG-encoded information signal includes a buffer memory in which the packets read from the record carrier are stored. The packets are retrieved from this buffer memory in response to the time stamps included in each packet for further processing in the MPEG decoder.
It is an object of the invention to provide an improved recording apparatus for recording a trick play signal, so that the buffer memory in the reproducing apparatus for reproducing a trick play signal can have a limited size.
The recording apparatus in accordance with the invention is characterized in that the time stamp generator means is adapted to generate subsequent time stamps in the form of subsequent cycles of (nxe2x80x2+kxe2x80x2)-bit count values, where nxe2x80x2 and kxe2x80x2 are integers larger than zero, a cycle of count values coinciding in time with the time interval equal to m1 revolutions of the head drum, the signal processing means being adapted to store a portion of a transport packet having a specific time stamp in a sync block having a specific sync block number, such that the said specific sync block number satisfies the following relationship,
NTPSBxe2x88x92q1 less than ATPSB less than NTPSB+q2,
where ATPSB is the specific sync block number included in the said sync block and NTPSB is a nominal sync block number, which has the following relationship with the said specific time stamp:
xe2x80x83NTPSB=int[(k+n/N)xc2x7q/M],
where k is the decimal value corresponding to the binary value of the kxe2x80x2 most significant bits of the count value corresponding to the said specific time stamp and n is the decimal value corresponding to the binary value of the nxe2x80x2 least significant bits of the count value of the said specific time stamp, N and M being positive integers and q being an integer for which holds qq1+q2.
The invention is based on the following recognition. Recording a trick play signal is done by recording segments of the information of the trick play signal in specific locations in groups of p tracks, such that upon reproduction in a trick play reproduction mode, where the record carrier speed equals n1 times the nominal reproduction speed, this nominal reproduction speed equaling the recording speed, exactly those segments are read by the read heads of the reproduction apparatus. The sync blocks in such segments include sync block numbers that have no relationship to the positions in the tracks where they are recorded. The question is: where to record the sync blocks comprising a packet of information of the first digital signal, such that it will be available upon reproduction in the trick play reproduction mode at the n1 times the nominal reproduction speed, at a time instant sufficiently in time for processing in the MPEG decoder, and not too long before this time, as in such case, the buffer memory may be too large.
In accordance with the invention, it has been realized that the packets are stored at such position in the tracks, in dependence of the time stamps generated for these packets and the sync block numbers given to the sync blocks in which those packets are stored, that a buffer memory of limited capacity suffices needed in the reproduction apparatus.
It should be noted that in a further aspect of the invention, for each trick play signal, the algorithm proposed is used for determining the exact positions of the sync blocks in the tracks, and thus their sync block numbers.